In a gas turbine engine the blades of the compressor can stall much in the same way as an airplane wing. When the relationship between the incoming air velocity and the speed of the blade creates too high an effective angle of attack the blade stalls and no longer pumps air. When a sufficient number of blades stall to affect the operation of the compressor, the phenomenon is known as surge.
During a surge of a gas turbine engine the combustor pressure immediately and sharply decreases. This occurs because the air is not being pumped into the combustor while the air in the combustor continues to exit through the turbine. Because of the decreased pressure in the combustor, a decrease in the energy delivered to the turbine immediately follows.
Surges can often occur during a ramped increase in power where the increase is too rapid for the particular conditions experienced by the engine. When a surge occurs under such operation the corrective action is to immediately decrease fuel flow until the surging stops, and then return to a power ramp which may be less steep than the original ramp.
It is important to detect these surges because of the high stresses and loads associated with them.
A prior method of detecting the surge includes sensing a decrease in the compressor discharge pressure. This is an acceptable method, but the parameter is not always available.
An alternate method of detecting compressor surge is desirable.